Re: [PATCH 3/2] memcg: Facilitate termination of memcg OOM victims.

Michal Hocko
2019-01-08T14:38:33Z

On Tue 08-01-19 23:21:23, Tetsuo Handa wrote:
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>
> If memcg OOM events in different domains are pending, already OOM-killed
> threads needlessly wait for pending memcg OOM events in different domains.
> An out_of_memory() call is slow because it involves printk(). With slow
> serial consoles, out_of_memory() might take more than a second. Therefore,
> allowing killed processes to quickly call mmput() from exit_mm() from
> do_exit() will help calling __mmput() (which can reclaim more memory than
> the OOM reaper can reclaim) quickly.

Can you post it separately out of this thread please? It is really a
separate topic and I do not want to end with back and forth without
making a further progress.

> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> ---
> mm/memcontrol.c | 17 +++++++++++------
> 1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 90eb2e2..a7d3ba9 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1389,14 +1389,19 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
> };
> bool ret = true;
>
> - mutex_lock(&oom_lock);
> -
> /*
> - * multi-threaded tasks might race with oom_reaper and gain
> - * MMF_OOM_SKIP before reaching out_of_memory which can lead
> - * to out_of_memory failure if the task is the last one in
> - * memcg which would be a false possitive failure reported
> + * Multi-threaded tasks might race with oom_reaper() and gain
> + * MMF_OOM_SKIP before reaching out_of_memory(). But if current
> + * thread was already killed or is ready to terminate, there is
> + * no need to call out_of_memory() nor wait for oom_reaoer() to
> + * set MMF_OOM_SKIP. These three checks minimize possibility of
> + * needlessly calling out_of_memory() and try to call exit_mm()
> + * as soon as possible.
> */
> + if (mutex_lock_killable(&oom_lock))
> + return true;
> + if (fatal_signal_pending(current))
> + goto unlock;
> if (tsk_is_oom_victim(current))
> goto unlock;
>
> --
> 1.8.3.1
>

--
Michal Hocko
SUSE Labs